1. Field of the Invention
The present invention relates to a sleeve and backseat configuration in a gate or globe valve and the method of manufacturing and installing that configuration.
2. Description of the Prior Art
In a typical gate valve or globe valve, the area between the bonnet and the stem has traditionally been filled with a packing material that seals the valve at that point. This area that is filled with the packing material, through which the stem of the valve moves in opening and closing the valve, is commonly referred to as a stuffing box. Over time, the stuffing box has been improved to improve the sealing means in that area. For example, U.S. Pat. No. 4,436,283 (Shore) discloses an improved gate valve which is suited for use in a horizontal or lie-down position. In Shore, a wave spring is employed in a gate valve in order to maintain a continuous resilient bias against the upstream seat utilized in the valve. Another improvement made to the seal in the stuffing box area was the addition of a backseat that is typically screwed into the bottom of the stuffing box. U.S. Pat. No. 3,003,744 (Fennema) and U.S. Pat. No. 3,275,290 (Siver) disclose such a backseat construction in a valve. Originally, the backseat was used as a fallback seal, thereby preventing a catastrophic failure of the valve upon failure of the packing material in the stuffing box.
In addition, the backseat itself has been the subject of improvements. U.S. Pat. No. 5,127,629 (Holliday) specifically discloses the improved sealing characteristics of a flexible metal backseat mounted on the valve stem, the set being sufficiently flexible to conform to a valve bonnet sealing surface. The backseat in Holliday engages a beveled portion of the bonnet when the valve is in the closed position.
The prior art does not, however, teach or disclose an extended portion of a backseat that forms a sleeve along the inner surface of a stuffing box. Additionally, the prior art does not teach or disclose any type of sleeve along the inner surface of the stuffing box area as a means of improving the seal and the longevity of the valve. The only known example in the prior art where the material of the stuffing box is different than the valve as a whole is disclosed in U.S. Pat. No. 3,032,310 (Hansen) wherein the stuffing box itself is a separate piece in a fabricated valve. The fabricated valve disclosed in Hansen is typically used in industry as a throwaway valve that cannot be refurbished because each of the fabricated pieces of the valve are typically joined in a manner that does not allow the valves to be refurbished and refitted.
The need to provide an even better seal in the stuffing box area has arisen as a result of increasingly stringent requirements regarding "fugitive emissions." Fugitive emissions are the result of leaks that occur at random points in valves, pipe joints, and unit operations through which fluids (gases and liquids) are transferred or stored. Generally, these types of emissions are prevalent in the stuffing box of a gate or globe valve because of the corrosion of the inner lining of the stuffing box. When the stem is raised or lowered in the operation of a valve, it will carry some of the product along the stuffing box and come in contact with the packing material therein. Over time, the corrosive nature of the material will cause pitting in the stuffing box as well as attack the packing material itself.
In the valve industry, there is a large domestic and international market for reworked and refitted valves in addition to the market for new valves. These valves are usually obtained when they are taken out of service and sold for scrap. They are also scavenged from old plants that are taken out of service altogether. The stuffing box of the used valves is almost always a problem area to refit because of damage due to corrosion. With the newly enacted, more restrictive, parameters for fugitive emissions under the recently amended Clean Air Act, there is also an urgent need to find a way to refit the used valves in a manner that allows these valves, once reworked and refitted, to meet the new requirements of the Act.
Because of the new strict federal regulations regarding fugitive emissions, there is an immediate need for a cost effective solution to containing such emissions in new, as well as reworked and refitted, gate and globe valves. The stuffing box area is the primary area where these emissions occur in gate and globe valves. The present invention solves this urgent problem by negating the corrosion that occurs in the inner lining of the stuffing box area while providing a better overall primary seal. It thereby virtually eliminates fugitive emissions from this problem area. In addition, the present invention provides a means for allowing reworked and refitted valves to meet the same standards under the Clean Air Act as new valves. That result for used valves would be virtually impossible, and, at a minimum, prohibitively expensive using current techniques in the valve refitting and refurbishing industry. The present invention therefore has the environmental benefit of allowing used valves to be refurbished to allow virtually no fugitive emissions. It also, by enabling the continued use by industry of refitted and refurbished valves, provides an additional environmental benefit because these reworked or refitted valves would otherwise find their way into landfills under the new Clean Air Act.